Method of producing hydrocarbons



June 9, 1959 k. v. HUGHES 2,889,880

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x770 le/yzy METHOD OF PRODUCING HYDROCARBONS Richard V. Hughes, Houston, Tex, assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application August 29, 1955, Serial No. 530,972

7 Claims. (Cl. 166-6) This invention relates to a method of extracting hydro carbons from an underground oil or gas reservoir and in particular concerns a method of maintaining and em hancing the production rate of desired reservoir fluids from a well without contamination by other reservoir fluids.

By way of illustration, in the customary manner of producing oil, a well is drilled into the producing formation and the oil flows either from open hole or through casing perforations into tubing by which it is carried to the surface. Desirably an oil well is completed so that it will produce oil only, but it is well known that in the course of time in water-drive oil fields many wells begin to produce salt water. It is well known that the mobile oil and water in the reservoir formation have been segregated by the forces of gravity into respectively the oilsaturated and the water-saturated parts. of the reservoir which are contiguous at the oil-water contact surface. The encroachment of water often results from what is termed water coning, which is a gradual conical rise in the oil-water contact surface about the well. When the apex of this conical rise of the oil-Water contact reaches the borehole or casing perforations, the well begins to produce salt water along with the oil and at the expense of oil production. Furthermore, when such water coning occurs the oil and water are apt to become emulsified and the breaking of such emulsion at the surface often times requires expensive equipment and chemicals. My invention provides a method for overcoming water coning in that my invention generates a depression in the oilwater contact which augments the production of oil instead of hindering it as does water coning.

In the application of my invention to a well such as that described above, salt water and oil are produced separately from the same well thus eliminating the formation of emulsion. My invention is particularly applicable in, but not restricted to, the Gulf Coast Area where oil often is produced from reservoir. sands which are thin and show little structural relief, such sands generally being under a strong water drive. In such sands the .producing wells are normally completed with shallow penetration. By the application of my invention to wells producing from such sands, the .oilaproducing zone around the wall is effectively thickened so that economic -oil production rates may be employed without danger of the well developing a water cone or producing water-contaminated oil.

My invention is also applicable to the production of oil from a well which penetrates the oil-bearing portion of a gas-cap type of oil reservoir. It is known that the commonly-used methods of completing and producing such a well eventually result in producing :free .gas along with the oil and the history of the well generally shows a gradually increasing gas-oil ratio which in time may restrict or eliminate the production of oil. By the application of my invention it is possible to augment the production of oil containing only solution gas from a well in a reservoir of this type.

Another application of my invention occurs when it is desired to produce gas from a water-drive reservoir in which there is little orsubstantially no oil zone. The

2,889,880 Fatented June 9, 1959 effect of water coning around a gas well penetrating a reservoir of this type may be eliminated by the use of my invention which also augments the production of water-free gas from such a Well.

A further application of my invention occurs in the case of a well which penetrates. a reservoir containing oil with a gas cap and having water underlying the zone of oil saturation. My invention augments the production of clean oil from such a reservoir, the oil produced by the use of my invention being uncontaminated with either free-gas or water.

My invention may be used to complete new wells or to recomplete old wells which have developed either a high 'water-oil ratio or, in cases of original or induced gas-cap fields, a high gas-oil ratio. My invention is applicable to either flowing, pumping, or other artificiallift wells. My invention is applicable to either a natural water-drive or a natural gas-cap drive reservoir and is also applicable to both primary and secondary recovery operations employing either water flood, or gas drive, or recycling of gas or water, or injection of other displacing fluids. My invention is applicable to a well that penetrates the respective fluid contact surface or surfaces of a reservoir containing gravity-segregated fluids in a common reservoir. As a result of the gravity segregation of the fluids, the respective fluid-saturated parts of the reservoir are found as contiguous layers.

In the application of my invention the respective gravity-segregated reservoir fluids are produced separately from the same reservoir through separate channels. in the well thus avoiding commingling of the fluids within 7 the well bore and in the flow string. By the application of my invention the production of uncontaminated, de-

sirable fluid is enhanced as a result of effectively thickenthe perforations opposite the displacing fluid.

. surface intersecting the well bore.

My invention may be more fully understood by reference to the drawings forming a part of this; specification, and in which Figure 1 shows a diagrammatical cross section of a conventional oil well in which water coning has developed;

'Figure 2 shows a diagrammatical cross section of a well employing my invention for the eflicient production of clean oil from a water-drive oil reservoir;

Figure 3 shows a diagrammatical cross section of a well employing my invention for the efficient production 'of gas from a water-drive gas reservoir;

Figure4 shows a diagrammatical cross section of a well employing my invention for the efficient production of -'oil from a gas-drive oil reservoir; and

Figure 5 shows a diagrammatical cross section of a well employing .my invention for the eflicient production of oil from a reservoir having a gas cap overlying the oil .and a water-saturated zone underlying the oil.

Referring to Figure 1, there is shown an oil well having casing 10 running from the surface of the ground to the bottom of the well. The well is shown as originally having been drilled through the entire producing sand section 14. Prior to completion of the well it was determined through electric logging, drill-stem or other tests that an oil-water contact surface intersected the well at the level 11, the reservoir sand 14 being oil saturated above the oil-water contact 11 and water saturated below the oil-water contact 11. Originally, that is prior to producing the well, the oil-water contact 11 is: a level In order to prevent undesirable production of water (displacing fluid) the lower end of the well is generally plugged with cement as at 12. Perforations 13 in the casing just below the top of the producing formation permit entry of oil (displaced fluid) from the oil-saturated sand 14. Tubing is set in the well with the annular space between tubing 15 and casing 10 packed off as at 16. The oil from the upper part of formation 14 enters the well through perforations 13 and flows upward through the tubing 15 to the surface. The rate of production may be con trolled by valve 18.

It is well known that for many producing sands, if thin as in the Gulf Coast area, production at almost any economic rate will very soon cause the well to produce salt water. This results from the well-known waterconing effect, i.e. the oil-water contact 11 cones upward as shown at 17 and the apex of the cone eventually reaches the perforations 13. When the apex of the water cone reaches the lowermost perforations 13, the well starts to produce salt water and may produce this water with the oil in the form of emulsion. The water must of course be separated from the oil at the surface before the oil can be sold. Water coning can be retarded or delayed by producing the oil at a reduced rate, but it is known that it will eventually occur in water-drive oil fields even at the most moderate rates of production, and especially in wells which produce from thin oil sands.

My invention and the manner in which it eliminates water coming in an oil well is illustrated in Figure 2. As in Figure l, the well is drilled through the producing formation and casing 20 is set through the formation 14. The casing is perforated at 23 in the oil-saturated interval above the original level of the oil-water contact 21 and is also perforated as at 22 in the water saturated interval some distance below the original oil-water contact. The oil-water contact is shown at 21 and its original level at the well bore may be determined by electric logs, drill-stem, or other tests. The well is completed in any of the well-known methods of dual completion. By way of example, there is shown in Figure 2 a packer 24 which is set at or somewhat below the level of the original oilwater contact 21. A second packer 26 is placed above the upper-most perforations 23. Tubing 28 is set in packer 24 and communicates with a cross-over joint indicated by 27 near the packer 26. The cross-over 27 is not shown in detail in Figure 2, but any known type may be used which serves to connect the tubing 28 with the annular space 29 in the upper part of the well. A second tubing 30 runs through the packer 26 to the surface. Alternatively two strings of tubing, either parallel or concentric, or other adaptations of tubing and the annulus may be used to convey the two flow streams to the surface if desired.

It is apparent that with the arrangement shown in Figure 2, oil from the upper or oil-saturated part of the formation 14 will pass through the perforations 23 and to the surface through the tubing 30 so that clean oil is delivered by connection 25. Salt water from the lower or watersaturated part of formation 14 will pass through the perforations 22, upward through the pipe 28 and cross over 27, and the annular space 29 to the surface connection 31. In this manner the water produced through perforations 22 is maintained out of contact with the oil which enters through perforations 23, and therefore no emulsion is formed. At the surface, the oil produced through tubing 30 and delivered at is sent to tankage, whereas the salt water produced through connection 31 is sent to a conventional water-disposal system. .Valve 19 is placed in the connection 25 so that the rate of flow of oil may be controlled. A similar valve 33 is placed in the connection 31 so that the rate of flow of Water may be controlled. While the means of controlling the flow is shown as a valve in the surface connection, it is to be understood that other equally-effective flow control means may be employed such as a surface choke or bottom-hole choke and if pumping or other artificial lift equipment is required for either or both fluids such means may comprise well-known means for controlling the production rate of either or both fluids.

The flow rate of the water and the flow rate of the oil are equivalent, irrespective of actual volumes, masses, or units of measurement, when the oil-water contact 21 remains substantially level about the well bore. To increase the effective thickness of the oil-producing section opposite the perforations 23, water is produced from the lower part of the formation through perforations 22 at a higher equivalent rate than oil is produced from the upper part through perforations 23. The effect of the higher rate of water production will be to produce a conical depression of the oil-water contact such as is shown by 32. This may eventually result in the production of some oil through the perforations 22 and when this condition is reached the water production is reduced somewhat so that it is just short of bringing oil into the saltwater system. Once steady-state flow conditions are reached within the reservoir sands about the well bore the rate of water production is maintained at a rate just short of that rate which would cause the inverted oil cone to reach the water perforations 22. If desired, the proper rate of water production corresponding to any desired rate of oil production could be adjusted and maintained through valves 19 and 33, or other means of control, activated by well-known automatic devices for detecting contamination in the flow lines. Under these conditions the oil produced through perforations 23 will be clean oil and will be uncontaminated with water. Inasmuch as the oil-producing section of the sand 14 has been effectively increased at the well bore, it is possible to add additional perforations 23 and thus augment the rate of clean oil production.

Whereas Figure 2 shows one form of equipment in the well by which production of water is accomplished independently of the production of oil, it is apparent that other apparatus for accomplishing this purpose may be employed. Dual completion practices are well known for flowing wells, and known dual pumping equipment may be employed in wells which require artificial lift. It is furthermore contemplated that the two flow channels need not literally be produced simultaneously, but may be produced alternately over short time intervals during which time interval there is no substantial movement of the oil-water interface. Apparatus for alternately pumping dual completion wells is well known. My invention may be applied to new wells or to recompleted old wells which have developed a high water-oil ratio. Furthermore, my invention is also applicable to Wells in a reservoir which is being water flooded as well as to those in which natural water-drives are active.

My invention may in similar manner be applied to a water-drive gas well as illustrated in Figure 3. The well is drilled through the producing formation 40 and through the original gas-water "contact whose original level is determined by well-known methods. The casing 41 is set through the formation 40 to a point considerably below the original level of the original gas-water contact. The casing is perforated at 43 in the gas-saturated interval above the level of the gas-water contact and is also perforated as at 42 some distance below the gas-water contact. The gas-water contact is indicated at 44 but originally this was a substantially level surface. A packer 45 is set just above the perforations 42, and tubing 46 with cross-over 47 connects the perforations 42 with the annular space 48 of the upper part of the casing. The tubing 49 is set through the packer 50 located above the perforations 43 and leads to the surface connection 51. Surface connection 52 communicates with the annular space 48. This manner of dual completion permits water (the dis- I placing fluid) to be produced through perforations 42 and gas (the displaced fluid) through the perforations 43,

without comrrnngling of the gas and water. Water is produced through perforations 42 at a rate suflicient to generate a depression in the gas-water contact as shown at 53. The rate of water production is adjusted manually or by automatic controls to be somewhat less than that which results in drawing gas into the perforations 42. The respective rates of production are controlled by valves 34 and 35 or other equivalent means.

The gas-producing section of the well is increased by my invention and the gas is produced without commingled water. Due to the relatively'high viscosity of the water compared to that of gas, the rate of water production to effect a substantial depression 53 of the gas-water contact is not large. The flow rate of the water and the flow rate of the gas are equivalent, irrespective of actual volumes or other units of measurement, when the gas-water contact remains substantially level about the well bore. Generation of the depression 53 merely requires that the water-production rate is higher than its equivalent rate.

The application of my invention to a gas-drive oil well is illustrated in Figure 4. In this case the producing formation 60 is gas saturated in its upper levels and oil saturated below the gas-oil contact. The well is drilled to considerable distance below the gas-oil contact whose original level may be determined by well-known methods. The casing 61 is set to a point below the gas-oil contact and is perforated at 63 in the gas zone near the top of the producing formation 60 and also at 62 in the oil zone below the gas-oil contact. A packer 65 is set between the two sets of perforations and oil tubing 66 is set through packer 65 and runs to the surface connection 67. Surface connection 69 communicates with the annular space 68 and the perforations 63 through which gas (the displacing fluid) is produced from the gas-saturated zone of the formation 60. Oil (the displaced fluid) is produced from the oil-saturated part of the formation 60 through the perforations 62 and the tubing 66. The respective production rates are controlled manually or automatically by valves 54 and 55 or other equivalent means.

In a completion of the general type shown in Figure 4, it is common practice not to produce the gas and in fact the perforations 63 are generally avoided. In this case the originally level surface of the gas-oil contact 64 is depressed (not shown in Figure 4) around the well and the apex of the conical depression eventually reaches the uppermost of the perforations 62 whereupon the well begins to produce large amounts of gas, i.e. it develops a high gas-oil ratio. This condition can be avoided or corrected by my invention in which gas is deliberately produced through perforations 63 at a rate somewhat higher than its equivalent rate, and just under that rate which would cause the upstanding oil cone shown at 70 in Figure 4 (instead of a depressed cone) to reach gas perforations 63. The flow rates of the gas and the oil are equivalent, irrespective of actual volumes or units of measurement, when the gas-oil contact remains substan tially level about the well bore. Consequently the oil produced through the perforations 62 contains no free gas and furthermore the thickness of the oil zone at the well is effectively increased.

It is apparent that my invention can be applied to new wells or to recomplete old wells which have developed high free gas-oil ratios. Furthermore, my invention is applicable to wells in a .gas-repressured reservoir as well as those in a natural gas-drive reservoir.

It is further contemplated that my invention as illustrated in Figures 2 and 4 may be combined for advantageously producing oil from a reservoir having a gas cap as shown in Figure 4 and also having water underlying the oil as shown in Figure 2. Such a situation is shown in Figure 5. The casing is perforated in the gas-saturated zone, in the oil-saturated zone, and in the water-saturated zone. Referring to Figure 5, the well having casing 81 penetrates the producing formation 80. The formation 80 is shown as having a gas-oil contact 82 and an oil- 6 water contact 83, the original level of these contacts at the well having been determined by customary methods. A packer 84 is set at or somewhat abovethe gas-oil contact 82, and a second packer 85 is set at or slightly below the oil-water contact 83. The casing is perforated at 86 in the gas-saturated zone above the packer 84, also at 87 in the oil-saturated zone between the two packers, and also at 88 in the water-saturated zone below thepacker 85. Tubing 90 is run through the packer 85, passing through the packer 84, and communicates with the surface connection 89. Tubing 91 is run through the packer 84 only and communicates with surface connection 92. The annular space 93 communicates with the surface connection 94. The two tubing strings 90 and 91 are shown as parallel strings, but these could as well be concentric with appropriate connections at the packer 84 so that the annular space between the concentric (not shown) pipes 90 and 91 serves as the conduit connecting the perforations 97 to the surface connection 92.

The completion shown in Figure 5 permits the separate and independent production of gas, oil and water without commingling of these fluids. My invention makes it possible to effectively increase the thickness of the oilproducing zone, this being desirable because oil is usually the most valuable of these fluids. This is accomplished by removing gas (displacing fluid) from above the oil (displaced fluid) at a rate higher than its equivalent rate, and also by removing water (displacing fluid) from below the oil (displaced fluid) at a rate higher than its equivalent rate. The respective equivalent rates are as previously defined in connection with the descriptions of Figures 2 and 4. The respective production rates are controlled manually or automatically by means of valves 72, 73, and 74 or other equivalent means for any given rate of oil production.

It is to be understood that the various fluid contacts 21, 44, 64, 82 and 83 are shown deformed as effected by my invention and that these surfaces were originally level plane surfaces (not as shown). The oil-water contact shown in Figure 1 is that developed by the prior art manner of producing the well of Figure 1 and is not that effected by my invention.

The application of my invention is not limited to the particular types of well completion shown in the accompanyin-g drawings which are for purposes of illustration only. My invention may employ other completion methods whereby the fluids are segregated within the well bore opposite their respective productive horizons and are carried to the surface by any combination of separate flow channels utilizing one or more strings of tubing, either parallel or concentric, or the annulus with tubing. If desired, the wells may also be equipped with additional packers and flow channels to provide for independent production from another reservoir rock either above or below the reservoir to which my invention is applied.

It is to be further understood that the production, i.e. withdrawal, of the respective displacing and displaced fluids need not be literally simultaneous, but mustbe substantially so. The withdrawals must take place so nearly simultaneously that over any short time interval during which they are not literally simultaneous no appreciable movement or distortion of the related fluid interface occurs. The term simultaneous as used in the appended claims is meant to include such substantial sirnultaneity.

What I claim as my invention is:

l. A method of extracting oil from an underground reservoir containing gravity-segregated gas, oil and water and having a gas-oil contact surface and an underlying oil-water contact surface which comprises providing a well which penetrates the reservoir to below the oil-water contact, providing a first flow channel between the surface of the ground and a zone of the well in the reservoir above the gas-oil contact, providing a second separate flow channel between thesurface of the ground and "a zone of the well in the same reservoir intermediate the gas-oil contact and the water-oil contact, providing a third separate flow channel between the surface of the ground and a zone of the well in the same reservoir below the oil-water contact, withdrawing gas through said first flow channel from a region of the reservoir above the gas-oil contact, simultaneously withdrawing oil through said second flow channel from a region of the same reservoir intermediate the gas-oil contact and the oil-water contact,

and simultaneously withdrawing water through said third flow channel from a region of the same reservoir below the oil-water contact.

2. A method of extracting oil from an underground reservoir containing gravity-segregated gas, oil and water and having a gas-oil contact surface and an underlying oil-water contact surface which comprises providing a well which penetrates the reservoir to below the oil-water contact, providing a first flow channel between the surface of the ground and a zone of the well in the reservoir above the gas-oil contact, providing a second separate flow channel between the surface of the ground and a zone of the well in the same reservoir intermediate the gas-oil contact and the water-oil contact, providing a third separate flow channel between the surface of the ground and a zone of the well in the same reservoir below the oil-water contact, withdrawing oil through said second flow channel from a region of the reservoir intermediate the gas-oil contact and the oil-water contact, withdrawing water through said third flow channel from a region of the same reservoir below the oil-water contact at a rate sufiicient to depress the oil-water contact about the well bore, and simultaneously Withdrawing gas through said first flow channel from a region of the same reservoir above the gas-oil contact at a rate sufiicient to distort the gas-oil contact upward about the well bore.

3. A method of extracting oil from an underground reservoir containing gravity-segregated gas, oil and water and having a gas-oil contact surface and an underlying oilwater contact surface which comprises providing a well which penetrates the reservoir to below the oil-water contact, providing a first barrier in the well opposite the gasoil contact, providing a second barrier in the well opposite the oil-water contact, providing a first flow channel between the surface of the ground and a zone of the well in the reservoir above the gas-oil contact, providing a second separate flow channel between the surface of the ground and through the first barrier to a zone of the well in the same reservoir intermediate the gas-oil contact and the oil-water contact, providing a third separate flow channel between the surface of the ground and through the first and second barriers to a zone of the well in the same reservoir below the oil-water contact, withdrawing gas through said first flow channel from a region of the reservoir above the gas-oil contact, simultaneously withdrawing oil through said second flow channel from a region of the same reservoir intermediate the gas-oil contact and the oil-water contact, withdrawing water through said third flow channel from a region of the same reservoir below the oil-water contact, and adjusting the ratio of gas-withdrawal rate to oil-withdrawal rate to a value lying between that which causes gas to enter the second flow channel and that which causes oil to enter the first flow channel, and adjusting the ratio of water-withdrawal rate to oil-withdrawal rate to a value between that which causes water to enter the second fiow channel and that which causes oil to enter the third flow channel.

4. A method of extracting fluids from an underground producing formation having a contact surface between gravity-segregated fluids in a common reservoir, one of the fluids being less desirable than the other, which comprises providing a well which penetrates the reservoir formation to below the fluid contact, providing in the well at approximately the level of the fluid contact a barrier completely separating zones of the borehole wall respectively above and below the fluid contact, providing tion above the barrier, providing a second flow channel separate from the first flow channel between the surface of the ground and a zone of the borehole wall in the same reservoir formation below the barrier, withdrawing a first fluid through the first flow channel, simultaneously withdrawing a second fluid through the second flow channel, and adjusting the rate of withdrawal of the lessdesirable fluid to be just under that rate which causes the more-desirable fluid to become entrained with the less-desirable fluid withdrawn.

5. A method of extracting fluids from an underground producing formation containing gravity-segregated oil and water in a common reservoir and having an oil-water contact surface in the reservoir formation which comprises providing a well which penetrates the reservoir formation to below the oil-water contact, providing in the well at approximately the level of the oil-water contact a barrier completely separating zones of the borehole wall respectively above and below the fluid contact, providing a first flow channel between the surface of the ground and a zone of the borehole wall in the reservoir formation above the barrier, providing a second flow channel separate from the first flow channel between the surface of the ground and a zone of the borehole wall in the same reservoir formation below the barrier, withdrawing oil through the first flow channel, simultaneously withdrawing water through the second fiow channel at a rate just under that rate which causes oil to become entrained with the water withdrawn.

6. A method of extracting fluids from an underground producing formation containing gravity-segregated gas and water in a common reservoir formation which comprises providing a well which penetrates the reservoir formation to below the gas-water contact, providing in withdrawing water through the second flow channel at a rate just under that rate which causes gas to become entrained with the water withdrawn.

7. A method of extracting fluids from an underground producing formation containing gravity-segregated gas and oil in a common reservoir and having a gas-oil contact surface in the reservoir formation which comprises providing a well which penetrates the reservoir formation to below the gas-oil contact, providing in the well at approximately the level of the gas-oil contact a barrier completely separating zones of the borehole wall respectively above and below the fluid contact, providing a first flow channel between the surface of the ground and a zone of the borehole wall in the reservoir formation above the barrier, providing a second flow channel separate from the first flow channel between the surface of the ground and a zone of the borehole wall in the same reservoir formation below the barrier, withdrawing oil through the second flow channel, simultaneously withdrawing gas through the first flow channel at a rate just under that rate which causes oil to become entrained with the gas withdrawn.

References Cited in the file of this patent UNITED STATES PATENTS 1,644,748 Schweiger Oct. 11, 1927 1,723,682 Deming Aug. 6, 1929 2,341,359 Buckley Feb. 8, 1944 

1. A METHOD OF EXTRACTING OIL FROM AN UNDERGROUND RESERVOIR CONTAINING GRAVITY-SEGREGATED GAS, OIL AND WATER AND HAVING A GAS-OIL CONTACT SURFACE AND AN UNDERLYING OIL-WATER CONTACT SURFACE WHICH COMPRISES PROVIDING A WELL WHICH PENETRATES THE RESERVOIR TO BELOW THE OIL-WATER CONTACT, PROVIDING A FIRST FLOW CHANNEL BETWEEN THE SURFACE OF THE GROUND AND A ZONE OF THE WELL IN THE RESERVOIR ABOVE THE GAS-OIL CONTACT, PROVIDING A SECOND SEPARATE FLOW CHANNEL BETWEEN THE SURFACE OF THE GROUND AND A ZONE OF THE WELL IN THE SAME RESERVOIR INTERMEDIATE THE GAS-OIL CONTACT AND THE WATER-OIL CONTACT, PROVIDING A THIRD SEPARATE FLOW CHANNEL BETWEEN THE SURFACE OF THE GROUND 